Scour is a severe problem that results in millions of dollars of damage to infrastructure and loss of life annually. Scour occurs during times of high tides, hurricanes, rapid river flow and icing conditions when sediment, including rocks, gravel, sand, and silt are transported by the currents, undermining bridge pier foundations, submarine utility cables and pipelines, and filling in navigational channels. Scour is dynamic; ablation and deposition can occur during the same high-energy hydrodynamic event, so the worst-case net effect cannot be easily predicted nor previously monitored in real-time.
Several bridge scour monitoring technologies exist, including several patented electromagnetic sensors, including U.S. Pat. No. 5,784,338, Time Domain Reflectometry System for Real-Time Bridge Scour Detection and Monitoring, to Yankielun, N. E. and L. Zabilansky, Jul. 21, 1998; U.S. Pat. No. 5,790,471, Water/Sediment Interface Monitoring System Using Frequency Modulated Continuous Wave, to Yankielun and Zabilansky Aug. 4, 1998; and U.S. Pat. No. 6,084,393, Scour Probe Assembly, to Yankielun, Jul. 4, 2000.
These technologies, employing metallic time domain reflectometry (TDR) and frequency-modulated continuous wave FM-CW reflectometry have proved highly successful in detecting, monitoring and measuring scour and deposition of sediments in freshwater. However, they are of limited utility, or even unusable in conductive media such as brackish water, seawater, or in clays and some contaminated soils. Consequently, the technologies may be deployed only in inland (fresh) bodies of water having sediments comprising non-cohesive (non-clay-based) soils.
Dr. Yankielun developed an optical TDR-based (OTDR) scour probe that relies on “micro-bending” in an optical fiber. This micro-bending is caused by the impinging pressure of sediments on a specially configured optical fiber to indicate the extent of scour depth. The technology is described in U.S. Pat. No. 6,526,189, Scour Sensor Assembly, to Yankielun, Feb. 25, 2003. While circumventing the problems encountered by conventional metallic TDR in saline waters and cohesive soils, the system uses an expensive OTDR unit.
An embodiment of the present invention employs an optical reflection coefficient-based technique. See U.S. published patent application 20030117154 A1, Method and Instrument for Electronically Recording and Imaging Representations of the Interaction of an Object with Its Environment, by Yankielun and J. H. Clark, Jun. 26, 2003, incorporated herein by reference. Using this technique, one may detect, monitor and measure sediment transport in conductive water/sediment environments economically, continuously and in real-time.
This new technology improves the ability to perform sediment transport research, monitoring, and measurement in coastal zones, saltwater estuaries, embayments and other highly conductive waters, especially in cold regions and in the presence of ice. The system is not only applicable to saline and highly conductive environments but will function as well in freshwater regimes.